Process of producing self-annealed cast-iron castings in permanent molds by the heat of the metal cast



Patented Maya, 1925;

UNITED STATES H. MELOCHE, OF DETROIT, INIICHIGAN, ASSIGNOR TO EARLHOLLEY, OF

DETROIT, MICHIGAN. I

PATENT OFFICE.

PROCESS OF PRODUCING SELF-ANNEALED CAST-IRON CASTINGS IN PERMANENTIIOLDS .BY THE HEAT OF THE METAL CAST;

I No Drawing.

To all, whom it may concern."

Be it know'nthat I, DANIEL H. MnLooHn, a citizen' of the United-States,residing at 2241Gladston'e Ave.,'Detroit, in the county of Wayne andState of Michigan, have invented certain new and useful Improvements inProcesses of Producing Self-Annealed Cast-Iron Castings in PermanentMolds by the Heat of the Metal Gust, of

. molded surfaces of the dry sand mold find 10 which the following is aspecification. In order to produce homogeneous castings (i. e., castingsof uniform hardness) in permanent moldsI have found it necessary inaddition to the precautions taken when casting in sand to protect thesurface of the mold with a refractory, inert and heat insulating paintwhich is very adhesive, and having protected it-to cover it with a thickcoating .of lamp black so that the casting when ejected has, alreadybeen practically annealed.

In order to make thecontinuous casting of greyiron castings in permanentmolds a commercial success it is necessary to eject them above thecritical temperature of cast iron, that is to say at a temperature ofabout 1650 F. which is 200 above'the critical temperature. In order toget clear definition the iron must'be' poured at a good yellow-heat.That is to say it should be poured at a temperature in excess of 2200 F.These conditions arevery severe and great difficulty has beenexperienced heretofore in commercially producing castings bycontinuously pouring iron into permanent molds, the chief diiii-' cultybeing that the coating-flaked 01f, volatilizedor was otherwise washedoff bythe molten iron.

Whilst the actual casting operations must followeach *other in quicksuccession it is necessary-to avoid the sudden chilling of the iron inthe mold as otherwise the castings produced thereby" will beunmachinable. The effect of a sudden chill is to solidify the outersurface and leave the core liquid. Unfortunately the cooling of theinterior will not provide sufiicient heat to 5 universally found thatonce hard spots-have been formed in the casting by chilllng onlyprolonged annealing will remove these hard softenthe skin by annealingas it has been App1ication filed December 26, 1922. Serial No. 609,145.t

The process I have invented consists as follows. The molds are eachproduced from a dry sand mold and' dry Isand core, the

core being liberally protected with graphite and dusted with lycopodium.A rib is cast around the iron molds so -as.to facilitate machining thesurfaces which match togather as set forth in U. S; patent to Phillips,#1,099,997, of June 16,- 1914. These molds are first cleaned and. facedup so that they will match together. The molds are then heated toapproximately 350 F. and coated with a refractory paint which isnon-volatile at any temperatureatwhich the iron is cast.

The molds are mounted on...;a horizontal rotating table with theirdividing planes normal to axis of rotation as set forth in co-pendingapplication, Serial No. 504,988, of Oct. 3, 1921, De Forest W. Candler.The

Wane, $751,083,122 of- Dec. 30, 1913.

The iron cast in the iron mold has to be somewhat higher insilicon thanmany commercial cast irons, thus corresponding to the higher grade castiron commonly known as #1 foundry iron. This iron has a silicon contentgreater than 2.75% and a manganese content lower than 0.40%. The totalcarbon content in this iron'runs from 2.50% to'3.50% andthe combinedcarbon of the pig is lessthan .7%. The sulphur and phosphorus are bothheld at a low figure as sulphur and phosphorus are both objectionablefor the same reason that they are objectionable in sand castings.

In melting this itl ffoundry iron it is preferable not to add more than10% low carbon scrap -(,20% to .30% C.) and the blast is so regulatedthat'the melting zone is confined to a few inches, so that the iron doesnot have an appreciable percentage of oxygen in it and also to avoidproducing combined carbon by the chilling effect of an excessivelystrong blast of air. I have dis-v covered that in this connection oncecombined carbon is formed in molten iron the castings'produced therefromare not as soft as castings produced from iron in which the carbon ismerely in solution and not chemically combined with the iron."

When pouring the iron in the mold the operations are repeated every twoor three minutes when making a three to five pound casting. This rate isregulated by the heating effect of the molten iron upon the mold hencewith larger castings a longer period of time would be allowed. In orderto keep the temperature of the mold below 1000 F. and in order toprotect the surface of the mold the refractory paint referred to aboveis used. The coating I prefer to use is that described in my co-pendingapplication, Serial No. 581,239, filed August 11, 1922. This coatingconsists essentially of fire clay with a little soluble silicate (ofsodium) as a binder. A coating of 1/64 (approximately) is applied to themold, the mold being heated so as to evaporate the water which is usedas a carrier for the fire clay and a solvent for the sodium silicate.

Above the coating of refractory fire clay a thick layer of lamp black isapplied. This coating of lamp black or carbon black is so thick thatafter the casting is ejected from the mold the lamp black coating isstill intact.

The result of following this procedure is that the molten iron flowinginto the mold, automatically heats the molds during the continuousoperation of the process to approximately 800 F. to 1000 F. and causesthe carbon coating of the mold to be partially removed either byabsorption or combustion. The carbon coating whilst not refractory is anexcellent insulator. The com-- bustion of thecarbon coating evolvesconsiderable heat, the combustion of even onetenth of an ounce percasting evolving sufficient heat to raise the temperatureof a 2% poundcasting no less than 280 F. The coating of carbon being pulverulent andnot compact like the fire clay coating already referred to, provides initself aneasy vent for the air in the mold. This air, of course, as 1tescapes, causes the lam black to burn which evolves heat as alrea ypointed out. The net results of the combined insulating qualities of thefire clay and the lamp black and the heat evolved by the lamp blackwhich is consumed results in the casting remaining red hotfor a muchgreater period of time than is the case when no lamp black is used.Further, the outer surface of the iron probably dissolves some of thecarbon and hence lowers its melting point and thus still further retardsthe cooling rate as molten iron is a relatively poor heat conductor. Byprolonging the period during which the Iron is red hot or rather duringthe period duringwhich it is molten more time is given to permit thesilicon to complete the reci itation of the carbon in the ll'OIl and tere y produce the soft grey iron which is the object sought for in thisprocess.

If iron is rapidly cooled a cbnsiderable proportion of carbon remains insolution when in the solid state. This solid solution increases thehardness and renders the casting brittle. Further, by prolonging themolten stage one secures complete filling of the mold.

lVithout the adherent refractory insulating inner coating the relativelythick outer lining of lamp b ack will not adhere because without theadherent insulating coating the mold becomes red hot and burns thecarbon Off. With the insulating refractory coating the temperature ofthe mold is held below 1250 F. a

I have noticed that when the casting is ejected that there immediatelyforms on the surface of the casting a. thin scale which falls oif whenthe castings are tumbled. This scale is'not formed unless an excess oflamp black is used. In other words, unless the coating of lamp black isintact when the castings are ejected from the mold.

The surface left when this scale drops off is quite soft and annealed.If no scale is formed, as happens when insuflicient or no lamp black isused, then the castings are hard. Whatever may be the'conneotion betweenthe formation of this scale and the resulting casting the fact is thatby using an excess of lamp black superimposed on an inert insulatingrefractory adherent coating self-annealed castings are produced which isthe object of this invention.

The successful operation of this 'proces depends upon the rate ofcooling o'fthe iron. The rate of cooling of the iron is determined 1.The temperature of the iron cast.

2 The temperature of the iron molds.

3. By the thickness of the walls of the iron molds. v

4. The insulating qualities of the refractory lining of the molds.

5. The thickness of the lamp black coat- Tn the commercial production oflarge quantities of two pound castings having sections varying from toin thickness, with a hollow iron mold operating at a working temperatureof 900 F. and having a wall thickness and a 1/64" refractory lining,together with a coating of lampblack, will solidify this casting intwenty seconds, which is the period of time which gives the mostdesirable results. With larger castings the conditions should beadjusted so that the period of time taken to solidify does not greatlyexceed this twenty seconds and with smaller castings the conditionsshould be varied so that the time of solidification is not much lessthan this period of twenty seconds.

What I claim is:

1. The process of producing self-annealed gray iron castings, whichconsists in casting the metal in moldscoated with a smooth adherentinert insulating refractory material and having a superimposed layer ofamorphous carbon'sufficiently thick to considerably prolong the coolingperiod of the casting.

2. The continuous process ofproducing self-annealed grey iron castingsin metal molds which consists in heating the molds then painting thesurface of the mold with a wash in Whicha heat-resisting adhesive isdissolved and an inert refractory substance is suspended and thencoating the mold with a relative thick coating of amorphous carbon,holding the molds closed by a yielding pressure, pouring iron into themolds, ejecting the castings above the critical temperature andmaintaining at all times an excess of lamp black so that at all timesafter the ejection of the casting the coating of lamp black remainspractically intact. I

3. The continuous process of producing self-annealed grey iron castings,which con-' sists in heating the molds to 400 F., then painting the moldsurfaces with a. permanent coating of an adherent inert instrlatingrefractory, then applying athick renewable coating of amorphous carbonof such a thickness that it is practically intact after the ejection ofthe casting, so thatat all times thecasings are cast in an excess oflamp black, then permitting the temperature of the molds to reach 1000F. and ejecting the castings whilst they are still above the criticaltemperature of 1450 F.

4. The continuous process of producing self-annealed grey iron castingsin permanent molds, which consists in melting iron having a compositionoffrom 2.50 to.3.75% carbon and from 1.75 to 2.75% silicon and pouringat a temperature in excess of 2200 F. into metal molds having apermanent adherent refractory coating of fire clay and a renewablecoating of lamp black, maintain ing the coating of amorphous carbon atsuch a thickness that it is intact after the castiiigs are ejected fromthe molds, ejecting the castings from the molds immediately they aresolid and permitting the molds to" be-v come heated to a temperatureabove 1000 F.

5. The continuous process of producing self-annealed grey iron castingsi-n jpermanent molds. which consists of first heating the metal molds toa temperature in excess of 400 F., then painting the metal molds with arefractory inert insulating coating mixed with a temperature-resistingadhesive, then applying a thick coating of amorphous carbon andmaintaining the carbon coating at such a thickness that it issubstantially intact at all times, second, melting iron of.

from 2.50 to 3.50% total carbon and of from 1.75 to 2.75% silicon,pouring the iron into the molds and finally ejecting the castings fromthe molds the moment they have sufficiently solidified.

6. The continuous process of producing self-annealed grey iron castingsin permanent molds having substantially the same composition as the ironcast therein, con

total carbon and from 1.75 to 2.75% silicon,

pouring the iron into the molds and finally ejecting the castings fromthe molds at a temperature greater than 1450 F. and permitting the moldsto reach a temperature in excess of 1000 F.

7. The continuous process of producing self-annealed grey iron castingsin pcrmanent molds, which consists in pouring iron at over 2200 F. intomolds protected by an adherent inert refractory insulating coatingand asuperimposed lining of amorphous carbon sufliciently thick so that itwill be substantially intact when the casting is removed, whereby theheat of the metal cast is retained within the casting and thesolidification of the casting is delayed.

8. The continuous process of producing self-annealed grey iron castingsin pcrmanent molds, which consists in pouring iron containing not over10% low carbon scrap at a temperature in excess of 2200 F. into metalmolds coated with an adherent inert refractory insulating coating and asuperimposed lining of amorphous carbon maintained sufliciently thick sothat it will be substantially intact after each. casting is ejected,whereby the heat ol' the metal cast is maintained within the casting.

9. The continuous process of producing self-annealed grey iron castingsin perinanent molds, which consists in pouring iron substantially freefrom oxygen at a temperature in excess of 2200 F. into molds protectedby an adherent inert refractory insulating coating and a superimposedlining of amorphous carbon sufficiently thick so as to be substantiallyintact when the casting is removed, whereby the heat of the metal castis retained within the casting.

10. The continuous process of producing self-annealed gray iron castingsin hollow metal molds, which consists in pouring iron at over 2200 F.into the said hollow molds, the walls of which are protected by anadherent, inert, refractory,,insulating coating and a superimposedlining of amor hous car-' ing and a superimposed lining of amorphouscarbon sufiiciently thick so that a casting weighing two pounds willtake r twenty seconds to solidify so that it may be ejected from themolds.

12. ,The continuous process of producing self-annealed gray ironcastings which consists in pouring molten iron into heated iron moldshaving a wall thickness of protected with an adherent, refractory,insulat- I v I 1 ng llning of with a super-imposed coating of lampblackthick, whereby a casting weighing two pounds solidifies in twentyseconds.

13. The process of producing iron castings in metal molds, comprisingthe coatin of the walls of the molds with a layer 0 amorphous carbon ofsuch a thickness as to appreciably prolong the period of solidification.Y Y

. 14. Theprocess of producing iron cast-- ings in metal molds,comprising the coating of the walls of the molds by means of a smokyflame so as to deposit thereona layer of amorphous carbon of such athickness as to appreciably prolong the period of solidification.

15. The process of producing iron castings in relatively permanent moldscomprising the coating of the walls of the mold with a layer ofamorphous carbon, of such thickness as to appreciably prolong the periodof solidification.

In testimony whereof I aflix my signature.

DAN IEDI-I. MELOCHE.

